Surgical loupes have been used for decades to more easily allow the surgeon to view small tissue structures or objects. One field of use for surgical loupes is neurosurgery. A surgeon is required to manipulate tiny nerve tissue structures for prolonged periods of time during surgery. A surgical loupes system can magnify the nerve tissues and make it easier for the surgeon to distinguish between different structures. Also, procedures can be accomplished that would be near impossible with the unaided eye.
Surgical loupes, in addition to magnifying the object of interest, also allow the surgeon to view the object of interest at a comfortable distance. For instance, small print in a document can be magnified and hence read by holding the document close to your eyes. However, this produces a great strain on the eyes to focus on an object at such close proximity to the eyes. If the small print could be enlarged and viewed from a distance, the print could be read with minimal strain to the eyes. Surgical loupes accomplish this task, by viewing an object at a comfortable distance and magnifying the size of the object of interest.
Surgical loupes typically have two sets of magnifying optical assemblies housed within barrels, one set for each eye. The optical axes of the two optical assemblies converge to a point in space. This point is the theoretical location of the object to be viewed. It is important to maintain this convergence between the two optical assemblies in order to insure a high quality, stereoscopic image.
Current surgical loupes use either a Galilean or Keplerian telescope optical configuration for the optical assemblies within the barrels. The objective lens or lens system is a positive or converging lens in both the Galilean and Keplerian configurations. The eyepiece or lens system nearest the eye is a positive or converging lens in a Keplerian system and is a negative or diverging lens in a Galilean system. The Keplerian design is well suited for higher magnification, but requires a long barrel and an image inverting/reverting member to produce a high quality image with the correct orientation at the retinal plane of the eye. If the image inverting/reverting member was not included, the image entering the eye would be flipped vertically and left to right. Therefore, if the object of interest was an arrow pointing upward to the right, the image entering the eye would be an arrow pointing downward and to the left. The Galilean designs are shorter and lighter, but are limited in their magnification power. They also have a much larger objective lens than the Keplerian design, which increases the weight of the system.
Surgical loupes differ in how they are worn by the surgeon. The four most common mounting methods are listed in Table 1 along with a manufacturer of an example system.
TABLE 1 ______________________________________ Current Surgical Magnifier Categories Category Maker ______________________________________ Adjustable Head Mounted Systems Carl Zeiss, Inc. http:.backslash..backslash.www.zeiss.com Through-the-Eyeglass Lens Designs for Vision, Inc. Systems http:.backslash..backslash.www.designsforvision.com Adjustable Eyeglass Mounted Keeler Optics Systems http:.backslash..backslash.www.keelerusa.com Combination Systems LuxTec http:.backslash..backslash.www.luxtec.com ______________________________________
An adjustable head mounted system provides a band which fits around the head of the surgeon and has a set of surgical loupes attached to the band that can be positioned in front of the eyes of the surgeon. The loupes can be rotated up out the line of sight of the surgeon when not in use. Each loupe swivels about a common axis to allow the surgeon to adjust their separation relative to each other. This permits the loupes to be optimized for the pupil separation of the surgeon. The downward tilting of the loupes can also be adjusted. This permits a surgeon to adjust the declination angle of the surgical loupes.
A through-the-eyeglass lens system provides a normal pair of eyeglass frames, to eyeglass lenses with an aperture formed within each lens and a surgical loupe barrel disposed within each lens aperture. This type of system is not adjustable for different pupil separations or different tilting angles of the barrels. The pupil separation of the user must first be measured and then the lens apertures formed to match the measured pupil separation. If the surgeon is required to wear prescription eyewear, his prescription can be built into the magnification optics of the barrels.
An adjustable eyeglass mounted system provides a normal pair of eyeglass frames, eyeglass lenses and a surgical loupes system attached to the bridge of the eyeglass frames that can be positioned in front of the eyes of the surgeon. The loupes can be rotated up out the line of sight of the surgeon. The loupes are laterally adjustable to accommodate various pupil separations. An advantage of this system is that it works well for surgeons that already have to wear prescription eyewear. Because they can view through the loupes or flip the loupes up and view through their normal prescription which can be built into the eyeglass lenses.
The combination systems utilize both the head band and eyeglass frame technologies for mounting their loupes. These systems typically are adjustable and allow for the loupes to be rotated out of the line of sight of the user. In addition, these systems as well as the others might have light sources attached to them to illuminate the object of interest.
The loupes barrels in a surgical loupes system are typically tilted downward at a fixed angle. Although some systems allow the angle of tilt to be adjusted, the tilting of the barrels requires the surgeon to cast his/her eyes downward to see through the loupes. This tilting is required for two reasons. First, the subject matter to be viewed during surgery is typically lying on a table below the line of sight of the surgeon. Second, it is more comfortable, over the duration of surgery, for the surgeon to cast his/her eyes downward than tilting his/her head forward. The angle of tilt of the loupes barrels is referred to as the declination angle.
The declination angle of the loupes is defined as the angle between the support line of the loupes and the actual line of sight of the user through the loupes. The support line is generally parallel to the straight ahead line of sight of the surgeon. Therefore, the declination angle is a measurement of the angle by which the eyes of the surgeon are cast downward relative to looking straight ahead. In the case of eyeglass mounted systems, the support line is an imaginary line connecting the superior auricular crevice of the ear, the location at which the eyeglass frames rest on the ear, to the point on the nose where the eyeglass frames rest. Research has shown the ideal declination angle is different for all surgeons, but is in the range from 15.degree. to 44.degree. with a mean of 34.degree.. This means an average surgeon can cast their eyes downward 34.degree. for extended periods of time. However, this downward casting is not as comfortable as looking straight ahead or downward at a slight angle. A majority of through-the-eyeglass lens systems can achieve declination angles between 10.degree. and 22.degree.. Although some systems can achieve up to 45.degree.. A significant percentage of adjustable loupes are not able to achieve a declination angle greater than 34.degree..
When the declination angle of the surgical loupes does not match the ideal declination angle for a particular surgeon, or the desired subject matter is not in the field of view of the loupes, the surgeon compensates in two different ways. First, the surgeon will increase the downward casting of his/her eyes. Over prolonged periods of time, such as surgery, this will cause a straining of the intrinsic and extrinsic eye musculature. Second, the surgeon will tip his/her head forward and downward in order to see the subject matter through the loupes. Over prolonged periods of time, such as surgery, this will cause a straining of the head, neck and shoulder musculature. These additional strains on the musculature of the body increase fatigue and lead to potential risk of extended or permanent disabilities.
Current surgical loupes, although state of the art, have four main drawbacks. First, they require the surgeon to cast his/her eyes downward. This downward casting, although less physically demanding than head tilting, places undue strain on the body of the surgeon. Ideally the surgeon should be able to look straight ahead or downward at a slight angle. Second, the loupes do not always allow the surgeon to view the subject area they desire to view. The surgeon must compensate by leaning forward and/or tilting his/her head. Third, loupes that do not have an adjustable tilting or declination angle are not always matched to the ideal declination angle of the surgeon. Therefore, the surgeon must cast his/her eyes at an angle that does not match their ideal declination angle. This places added stress on the eyes of surgeons. Fourth, the location of the barrels limits the surgeon from seeing the object of interest non-magnified. This could limit the surgeon's ability to correlate the magnified image through the loupes with the overall surroundings of the object of interest.